1. Field of the Invention
The present invention relates to an electrophotographic photoconductor with excellent electric characteristics, abrasion resistance and durability and high photosensitivity, and polycarbonate resin for use therein.
2. Discussion of Background
Recently organic photoconductors are used in many copying machines and printers. These organic photoconductors have a layered structure comprising a charge generation layer (CGL) and a charge transport layer (CTL) which are successively overlaid on an electroconductive support. The charge transport layer (CTL) is a film-shaped layer comprising a low-molecular-weight charge transporting material (CTM) which is dissolved with a predetermined concentration in a binder resin. The addition of the charge generating material (CTM) to the binder resin lowers the intrinsic mechanical strength of the binder resin, so that the CTL film is fragile and has a low tensile strength. Such lowering of the mechanical strength of the CTL causes the wearing of the photoconductor and the peeling of the CTL away from the photoconductor or forms scratches and cracks in the surface of the photoconductor.
It has been proposed to polymerize the charge transporting material (CTM). For instance, M. Stolka et al. have proposed polyvinyl carbazole, polyvinyl anthracene, and polyvinyl pyrene as such polymerized charge transporting materials as reported in J. Polym. Sci. Vol 21.969. Vinyl polymers of hydrazone are described in Japan Hard Copy '89, page 67. Furthermore, polymerization of charge transporting materials (CTM) have been tried as disclosed in U.S. Pat. Nos. 4,801,517, 4,937,165, 4,959,288, 5,030,532, 5,034,296, and 5,080,989, and in Japanese Laid-Open Patent Applications 64-9964, 3-221522, 2-304456, 4-11627, 4-175337, 4-183719, 4-31404, and 4-133065. The polymerized charge transporting materials have not yet been used in practice.
M. A. Abkowitz et al. reported in PHYSICAL REVIEW B VOL46, 6705 that the drift mobility of a polymerized CTM is smaller by one figure than that of a charge transporting material comprising a low-molecular-weight CTM and a binder resin in which the low-molecular-weight CTM is dispersed. It is considered that this indicates that such a polymerized CTM is unsatisfactory for use in practice with respect to the photosensitivity and residual potential thereof.
Furthermore, there has been proposed a method comprising the steps of dispersing a low-molecular-weight CTM in a binder resin, and then curing the binder resin. This method, however, has not yet provided a practical solution to the problem of the wearing of the photoconductor because the CTM is detached from the binder resin due to the concentration of the CTM as high as 30 to 50 wt. % and the insufficient curing reaction of the binder resin.
Conventionally known representative aromatic polycarbonates are obtained by allowing 2,2-bis(4-hydroxyphenyl)propane (hereafter referred to as bisphenol A) to react with a carbonate precursor material such as phosgene or diphenylcarbonate. Such polycarbonates made from bisphenol A are used in many fields because of excellent characteristics, such as high transparency, high heat resistance and dimensional stability.
However, recently, there is a keen demand for an aromatic polycarbonate resin with higher heat resistance and better optical characteristics such as light transparency.
In order to obtain an aromatic polycarbonate resin having higher heat resistance than that of the conventional aromatic polycarbonate resins made from bisphenol A, varieties of aromatic polycarbonates have been proposed, which are produced by use of a bivalent phenol instead of bisphenol A.
However, such aromatic polycarbonates are not satisfactory for use in practice.